In a known design, a dome is mounted at its periphery to a support through a flexible surround which allows the dome to move axially. The edge of the dome is also coupled to a voice coil mounted in the gap between the poles of a permanent magnet, movement of the dome being caused by changes in the polarity of the electrical supply to the voice coil. Typically the dome is metallic, e.g. aluminum, and the voice coil is wound on a polymeric former suitably attached to the dome.
At low frequencies, the dome, subjected to a cyclic force from the voice coil, behaves as a rigid body with all points on its surface moving with the same axial velocity. At some higher frequency, known as the first break-up mode, however, the structure will exhibit a resonant mode where the central part of the dome moves axially while the edge of the dome moves radially. This point marks the high frequency limit of the driver and the aim of the loudspeaker designer is to maximize this value.